A web browser running on a client device may become compromised by a malicious attack, such as a man-in-the-browser attack. A man-in-the-browser attack may take advantage of vulnerabilities in the web browser's security to modify web pages, modify transaction content, or insert transactions using the identity of the user. A man-in-the-browser attack may be difficult to detect by a user of the web browser or a host server with which the client device communicates. A hacker may use a man-in-the-browser attack to capture information to harm the user, such as by learning the user's credit card information and using the credit card information to make unauthorized purchases, learning the user's banking information and using the banking information to withdraw funds, or the like.